Acceleration limiting means for fluid motors



Jan. 14, 1969 D. K. SKOOG 3,421,735

ACCELERATION LIMITING MEANS FOR FLUID MOTORS Filed Nov. 23, 1966 M I? 20 m F/G.

:3 INVENTOR A I I3 4 DONALD K. 5x000 United States Patent 3,421,735 ACCELERATION LIMITING MEANS FOR FLUID MOTORS Donald K. Skoog, Mountainside, N.J., assignor to Ingersoll-Rand Company, New York, N.Y., a corporation of New Jersey Filed Nov. 23, 1966, Ser. No. 596,605 U.S. Cl. 2531 13 Claims Int. Cl. F01d 17/04; F03!) 15/02; E21c 3/20 ABSTRACT OF THE DISCLOSURE The apparatus provides for a valve to be placed in either the exhaust line of the motor or a by-pass around the motor so that when the motor is subjected to sudden no-load conditions after a load condition, the supply of motive fluid to the motor is almost out off. When load conditions are present again, the valve allows full flow of fluid to the motor.

This invention relates to a system for rotating an apparatus and more particularly but not exclusively to a rotational system for a rock drill of the cam actuated type employing a hydraulic motor as the power supply. More specifically, this invention provides a device for controlling the supply of fluid to the hydraulic motor to prevent acceleration of the motor when the load is suddenly removed from the motor.

It has been discovered that in cam actuated rock drills, such as shown in US. Patent No. 3,186,498 and the US. application of E. H. Kurt and A. A. Buehler filed concurrently with this application on Nov. 23, 1966, and having Ser. No. 596,525 that when the hammer is released to deliver an impact to the drill steel, the motor will tend to accelerate. This sudden acceleration often results in breakage of either the cam or the casing thus requiring shut down of the drill.

It is therefore the principal object of this invention to provide a control for a hydraulic motor driven rock drill which will eliminate breakage of the cam and casing.

It is another object of this invention to provide a device which will prevent acceleration of a fluid motor when the load on the motor is suddenly removed.

In general, the aforementioned objects are carried out by providing a rock drill which includes a casing, a drill steel extending into the casing, a hammer mounted for reciprocal movement within said casing, integrated cam means and follower means for raisin-g and quickly releasing the hammer on rotation of one of the cam means and follower means. A system for rotating one of the cam means and follower means is provided which includes a fluid motor connected to one of the cam means and follower means having inlet and exhaust passages and being subjected to load and sudden no-load conditions, means for supplying motive fluid to the inlet passage for driving the hydraulic motor, and means connected to the motor for preventing acceleration of the motor substantially at the point when the load on the motor is suddenly removed.

These and other objects will become apparent from the following description and drawings wherein:

FIG. 1 is a schematic diagram of the present invention as used in a rock drill;

FIG. 2 is a detail of a portion of FIG. 1;

FIG. 3 is a detail of an alternative embodiment of this invention; and

FIG. 4 is a view of a cam profile and follower which may be used in a cam actuated rock drill.

Referring to FIG. 1 and the preferred embodiment of this invention there is shown a schematic diagram of the 3,421,735 Patented Jan. 14, 1969 present invention as used in a rock drill substantially similar to that of the previously mentioned application of E. H. Kurt and A. A. Buehler filed concurrently with this invention on Nov. 23, 1966, and having Ser. No. 596,525. There is a rock drill generally indicated at 1 including a hammer 3 which is rotated by a hydraulic motor 20 through mechanical linkage 23, 21 such as gearing. The motor 20 is driven by an engine driven pump 40. The rock drill 1 includes a casing 2 having a hammer 3 mounted for reciprocating an-d rotative movement within the casing 2. The hammer has an elongated extension 7 which is adapted to strike the drill steel 4 which extends into the casing 2. A cam 10 which is best shown by referring to FIG. 4 is integrated with the outer periphery of the hammer 3.

The cam includes a flat portion 14, a rise or incline 12 and a sudden drop 13. A pair of rollers 11 are mounted on the casing wall 2 and extend into the inside of the easing and engage the cam 10.

A chamber 5 is provided at one end of the casing 2 and is pressurized by a compressor 30 through valves 31 and 32 to lines 33 and 34. As is more specifically pointed out in the aforementioned application of E. H. Kurt and A. A. Buehler, the compressor 30 supplies compressed air to the chamber 5 at a constant rate to give an initial pressure in chamber 5. As the hammer is rotated by the motor 20 and raised by the cam and follower, the air is further compressed to provide a driving force to the hammer. If a greater impacting force is desired, the initial pressure in chamber 5 may be increased.

A variable delivery pump 40 which is driven by an engine 41 receives fluid from a reservoir 45 through line 46. The pump 40 pumps fluid through line 42, directional valve 43, inlet passage 24 to the hydraulic motor 20. The fluid will then pass out of the motor exhaust passage 25, through a rotary valve 22, to line 26, through the directional valve 43, and back to the reservoir 45 through line 44. A line 35 connects the chamber 5 through line 34 with the pump 40. There is a valve 36 of any suitable type which responds to the pressure in chamber 5 to control the pump 40. As the pressure in chamber 5 is increased, the pump 40 increases its delivery to motor 20 to in crease the speed of rotation of the hammer 3. A restriction may be placed in the line 35 to prevent rapid fluctuations in pressure.

Referring again to FIG. 4, as the hammer 3 is rotated, the cam 10 will also be rotated relative to the follower 11. If it is considered that the roller starts on the flat portion 14 of the cam 10 as the cam is rotated and the follower 11 moves along the rise 12, a load is placed on the hydraulic motor 2.0. This is because as the cam is rotated further while the follower is engaging the rise 12, the hammer 3 is moved into the chamber 5 and when the chamber is sealed, the hammer will begin compressing the air in that chamber. As the air in chamber 5 becomes more compressed, it is more difl'lcult for the hammer to be raised and therefore the hydraulic motor 20 must do more work. As the hammer is rotated further and the roller reaches sudden drop 13, the hammer is quickly released and the compressed air in the chamber 5 forces the hammer 3 toward the drill steel to deliver an impact, the load on the motor 20 is suddenly removed. The motor 20 will then remain under substantially no load conditions until the follower again engages the cam 10 and begins to raise the hammer again.

It has been found that the sudden removal of the load from a hydraulic motor will tend to result in the sudden acceleration of the motor. This is because there is a sudden increase in the amount of motive fluid supplied to the motor when the load is removed. During operation of the hammer, the pump 40 is supplying fluid to the motor 20 at a substantially constant rate. When a load is placed on the motor, pressure builds up in the inlet line of the motor. When the load is suddenly removed this pressure build up is released resulting in additional flow of fluid which causes the motor 20 to accelerate. The sudden, if brief, acceleration of the motor will cause the hammer 3 and cam to rotate faster than is desirable. As the cam is rotated faster, when the cam and follower engage each other at the point of impact, the cam will not strike the roller 11 on the fiat portion 14 but the cam will be rotated around so that the roller 11 engages the cam 10 on the rise 12. This has been found to be one of the principal causes of breakage of both cams and followers.

I have discovered that if the motor speed can be maintained substantially constant at or near the point where the load is suddenly removed, the hammer will not rotate far enough for the cam and follower to engage each other on the rise 12 of the cam and will substantially eliminate breakage. The hammer will rotate a certain amount due to inertia and this inertia must be considered in determining when the flow of fluid to the motor should be reduced.

A previous attempt has been made at preventing the motor from racing by placing a restriction on the downstream side of the motor. This was merely a flow control and was not tied in with the motor. It was believed that this would eliminate the sudden increase in motive fluid passing through the motor. However, it was discovered that during the first few cycles of the rock drill, the restriction did not eliminate the increase in flow of fluid and cam breakage often occurred during these first few cycles. The restriction would become effective after a number of cycles. If the cam or follower did not break down during the first few cycles, the rock drill functioned satisfactorily. However, in order to produce a marketable rock drill it is necessary that cam breakage be eliminated almost entirely. I have discovered that by using some means to cut off the flow of motive fluid at or near the point where the load is removed from the fluid motor, the motor will not tend to accelerate when the load is removed. This is true even during the [first few cycles of the rock drill. It is therefore believed that cam breakage due to aforementioned conditions can be eleminiated in its entirety.

Referring to FIGS. 1 and 2 and the preferred embodiment of this invention, I have placed a rotary valve 22 in the exhaust or downstream conduit 25, 26. This rotary valve is of any suitable type and includes a rotating element 27 having a passage therethrough and is mounted on the pivot or shaft 28. This valve is connected through suitable mechanical linkage 23 to the mechanical linkage 21 of the motor drive shaft. This mechanical linkage may be any suitable means such as gearing or a belt and pulley drive. By using this mechanical linkage to the motor drive shaft 21, the rotary valve is coordinated with the rotation of the hammer 3 and cam 10. Preferably, the valve element 27 is slightly smaller than the valve housing to provide a passage 29 around the element 27. This prevents complete shut off of the exhaust.

In operation the motive fluid flows from the reservoir 45, through the pump 40, inlet passage 24 and drives the motor 20. The exhaust fluid will then go through passage 25, valve 22, and passage 26 back to the reservoir. The valve is generally in the open posititon which is 90 degrees relative to the position of the valve element 27 shown in FIG. 2. It is in this position while the roller 11 and cam 10 are engaged on the flat portion 14 and rise 12 of the cam 10. These are the positions of load on the motor and full flow of fluid to the motor is required. As the cam is further rotated and the roller approaches the point A or sharp drop 13, the motor would normally tend to race because of a sudden drop in the load on the motor 20. The element 27 of the valve 22 is rotated by mechanical linkage 23 to the position shown in FIG. 2. This will result in a substantial blockage of the exhaust 25 of the motor 20 and will thus eliminate acceleration of the motor when the load is substantially removed. A small amount of fluid will flow through passage 29 when in this position to prevent pressure surges. The motor will not accelerate because the supply of motive fluid is restricted. The supply is restricted because the exhaust is substantially out 01f. The element 27 will remain in this position until the flat portion 14 of the cam 10 and roller 11 engage each other at which time the element 27 will be rotated an additional degrees relative to the position shown in FIG. 2 and the motor will begin operating at normal speed.

Referring to the embodiment shown in FIG. 3 the principle of operation is substantially the same as that of FIG. 2. In this instance, however, the means for preventing the motor from aceclerating when the load is substantially removed is placed in a by-pass conduit connected to the inlet conduit instead of being in the exhaust passage. As shown in FIG. 3 a valve 122, which is the same as the valve 22 of FIG. 2, is placed in a bypass conduit 126 which is connected to the exhaust passage 125 around the motor 120. The valve 122 includes a valve element 127 having a passage therethrough and is mounted on a pivot or shaft 128 and is mechanically coupled by suitable means 123 such as a gear or belt or pulley drive to the drive shaft 121 of the motor 120. In the embodiment of FIG. 3 the valve is connected to the drive shaft 121 of the motor so that it is closed when is operating under a load and open when the load is substantially removed.

The operation of the embodiment of FIG. 3 is as follows. When the cam 10 and roller 11 are engaged on the flat portion 14 and the rise 12 of the cam 10, the motor is operating under load. The valve 122 is in the closed position which is a position 90 degrees relative to that shown in FIG. 3. Fluid flows from the reservoir 45, to the motor driven pump 40, through the conduit 42, inlet passage 124 and to drive the motor 120. The motive fluid is then exhausted through passage 125, back through the directional valve 43 and to the reservoir 45. When the hammer and cam are rotated further and the roller reaches or approaches the point A and the sharp drop 13 of the cam 10 and the load on the motor is substantially removed, the element 127 of the valve 122 is rotated 90 degrees to the open position shown in FIG. 3 and most of the motive flui'd will flow through the by-pass 126 around the motor through the exhaust passage 125 and back to the reservoir.

It can readily be seen that when the supply of motive fluid such as oil to the driving motor 20 or 120 is substantially cut off, the hammer 3 will not tend to race when the load on the motor is suddenly removed.

The point at which the valve 22 or 122 should open or close, depending upon the embodiment used, to cut off fluid supply to the motor depends upon various factors. It may be desirable to shut the motor off right at the point A when the load is removed or it may be desirable to cut the motor 20 or 120 off at a point just before the load is removed and allow the momentum of the hammer to carry it across the point of change. This momentum will not be sufficient to cause the follower 11 and cam 10 to engage each other on the rise 12. In other drills it may be desirable to cut the motor off at some point after the load is removed such as when the roller is midway between the point A and the flat 14 on the cam 10.

Various factors should be considered in determining the point of cut 011. Some of these factors include the size of the drill, the impact to be delivered, the size of the drill steel used, and the size of the hammer. A larger hammer would result in more momentum and the cut off point should be before the point A so that it will be effective. If a smaller hammer is used it may be desirable to time the cut off point just at the drop ofi point because the inertia of the hammer is small and would not tend to rotate very much when supply of fluid to the motor is reduced. Other factors which should be considered include the amount of pressure in the chamber 5. As the pressure in chamber is increased, the hammer moves towards the drill steel faster and delivers a greater impact and the roller and cam would engage each other in less time. Additional factors which should be considered are the size of the motor, the speed at which it is to be rotated by the engine driven pump 40 and the size of the valve 22 or 122.

Although a mechanical coupling has been shown between the motor 20, hammer 3 and valve 22, other couplings may be desirable. Pneumatic, hydraulic, or electrical connections may be desirable to actuate the valve 22 or 122 at the proper time. The location of the valve 22 may be altered. Instead of being directly in line with the motor drive shaft 21, it may be desirable to have the valve 22 actuated directly by the cam 10. It is not intended that the particular actuating means or location of the valve 22 be a limiting factor.

It will be apparent from the foregoing description that the objects of this invention have been carried out. It is intended that the foregoing description be merely that of a preferred embodiment and that the invention not be limited in any way except by that which is within the scope of the appended claims.

I claim:

1. A system for driving an apparatus comprising:

a fluid motor operatively connected to said apparatus and being alternately subjected to load and sudden no-load conditions;

means for supplying motive fluid to said fluid motor;

and

means connected to and continuously operable by said fluid motor for substantially reducing the supply of motive fluid to said motor and preventing said fluid motor from accelerating when the motor is subjected to a sudden no-load condition.

2. The system of claim 1 wherein said motor has an exhaust passage and said acceleration preventing means is a normally open valve for substantially closing said exhaust passage substantially at the point when the load on said motor is suddenly removed.

3. The system of claim 2 wherein said valve is a rotary valve mounted within said exhaust passage and having a speed of rotation coordinated to the speed of rotation of said apparatus.

4. The system of claim 1 wherein said motor has an exhaust passage and said acceleration preventing means includes a by-pass means connecting said means for supplying motive fluid and exhaust passage around said motor and a normally closed valve for opening said bypass means substantially at the point when the load on said motor is suddenly removed.

5. The system of claim 4 wherein said valve is a rotary valve mounted within said by-pass means and having a speed of rotation coordinated to the speed of rotation of said apparatus.

6. In combination, a rock drill comprising a casing, a hammer reciprocally disposed within said casing for delivering an impact to a workpiece, integrated cam means and follower means for raising and quickly releasing said hammer upon rotation of one of said cam means and follower means, a fluid motor for rotating one of said cam means having inlet and exhaust passages; means for supplying motive fluid to said inlet passage for driving said motor, and means connected to and cooperating with said motor for preventing said motor from accelerating when said hammer is quickly released.

7. The rock drill of claim 6 wherein said fluid motor is a hydraulic motor.

8; The rock drill of claim 7 wherein said acceleration preventing means is a normally open valve for substantially closing said exhaust passage substantially at the point when said hammer is quickly released.

9. The rock drill of claim 8 wherein said valve is a rotary valve having a speed of rotation coordinated to the speed of rotation of one of said cam means and follower means.

10. The rock drill of claim 10 wherein said rotary valve is mechanically coupled to one of said cam means and follower means.

11. The rock drill of claim 7 wherein said acceleration preventing means includes by-pass means connecting said inlet and exhaust passages around said hydraulic motor and a normally closed valve for opening said by-pass means substantially at the point when the load on said motor is suddenly removed.

12. The rock drill of claim 11 wherein said valve is a rotary va'lve having a speed of rotation coordinated to the speed of rotation to one of said cam means and follower means.

13. The rock drill of claim 12 wherein said rotary valve is mechanically coupled to one of said cam means and follower means.

References Cited UNITED STATES PATENTS 2,938,501 5/1960 Titcomb 2531 3,107,083 10/1963 Pewthers 173-123 X 3,185,439 5/1965 Inaba et a1 2531 3,186,498 6/1965 Roll 173-123 3,322,208 5/1967 Skoog 173l23 EVERETTE A. POWELL, JR., Primary Examiner.

US. Cl. X.R. 91-76; 173123 

